Problem: Tiffany did 14 more jumping jacks than Christopher in the morning. Tiffany did 17 jumping jacks. How many jumping jacks did Christopher do?
Tiffany did 17 jumping jacks, and Christopher did 14 fewer than that, so find the difference. The difference is $17 - 14$ jumping jacks. She did $17 - 14 = 3$ jumping jacks.